In order to gain a better understanding of translation in eucaryotes, mutants affecting the translation apparatus of Saccharomyces cerevisiae, will be obtained and studied. We will concentrate on selecting mutants that affect the ribosome by using three different selection techniques. One approach relies upon omnipotent yeast nonsense suppressors, which have shown to cause altered ribosomes. By selecting for unlinked antisuppressor mutations that reduce the efficiency of these omnipotent suppressors, we hope to obtain new mutations affecting the ribosome. "Suppressors" of these antisuppressors may yield yet other ribosomal alterations. Finally, we will search for yeast ribosomal mutants among extragenic revertants of tRNA synthetase mutants, since this approach was successful in E. coli. The presumptive ribosomal mutants obtained will then be screened for phenotypic properties associated with ribosomal mutants such as cold, heat, or antibiotic sensitivity. Ribosomes from the most promising of these mutants will then be analyzed genetically and examined for alterations in in vitro protein synthesis as well as for altered ribosomal proteins. Mutations which cause altered ribosomes will then be placed on the genetic map. In addition, the in vivo levels of misreading will be compared in various mutants.